The present invention relates to a novel composition which is useful for performing improved liquid chromatography. More particularly, the present invention relates to an improved composition and method for performing anion-exchange chromatography wherein the stationary phase employed exhibits enhanced hydrolytic stability in a variety of eluent solutions, particularly alkaline solutions such as carbonate and/or bicarbonate solutions. The presently described compositions, therefore, allow one to perform anion-exchange chromatography over prolonged periods of time without significant loss of chromatography column performance.
Anion-exchange chromatography is a well known technique for the analysis and separation of anions from solutions wherein the technique typically includes a chromatographic separation step using an eluent solution containing an electrolyte. During the chromatographic separation step, ions of an introduced sample are eluted through a chromatography column which comprises an insoluble stationary phase to which functional anion-exchange groups are attached. Anions traversing through the column and contacting the stationary phase are then capable of exchanging at these positively-charged anion-exchange sites. For the most part, quaternary ammonium groups are employed as the principle functional group of anion-exchange chromatography.
Successful anion-exchange chromatography requires the use of eluents that may exhibit either an acidic or alkaline character, where the eluent may possess various degrees of acidity or alkalinity. Such a property of eluents, however, often has a deleterious effect on the hydrolytic stability of the groups which link the functional anion-exchange site to the insoluble stationary phase. As such, presently known anion-exchange chromatography columns are often usable for only a relatively short period of time, thereby significantly adding to the expense associated with high performance anion-exchange chromatography.
For example, the most common compounds employed for linkage to the stationary phase in anion-exchange columns are acrylate and methacrylate esters whose terminal epoxide groups have been functionalized to possess a quaternary ammonium anion-exchange site. More specifically, anion-exchange stationary phases are commonly prepared from the commercially available compound glycidyl methacrylate which has been functionalized to possess a terminal quaternary ammonium salt. Once functionalized, the glycidyl methacrylate-derived compound possesses a terminal quaternary ammonium anion-exchange site whose nitrogen atom is separated from an ester group which is internal to the backbone of the compound by a total of three carbon atoms. While anion-exchange columns employing such stationary phases have found use for anion-exchange chromatography, such columns are often less than economically practical due to their inherent hydrolytic instability.
Therefore, there is a need for novel compositions useful for anion-exchange chromatography which exhibit improved hydrolytic stability in the presence of various different eluent solutions.